1. Field of the Invention
The invention concerns an arc furnace with a furnace shell, a furnace lid with lid ring and a lid lifting and swivelling means. The furnace lid has a lid opening for exhausting the flue gases from the interior of the furnace, and a flue gas exhaust nozzle arranged above the lid opening for removing the flue gases.
2. Description of the Prior Art
The design of the flue gas exhaust nozzle and especially its arrangement with respect to the arc furnace is of particular importance, because it is on the one hand the connecting link in the exhaust removal system between the movable furnace vessel and the fixed exhaust line and on the other hand must be completely integrated into the individual operating steps of the furnace operation.
The following are the main operating steps in the operation of the arc furnace:
1. Charging. For this purpose, the furnace lid normally raised from the furnace vessel, is swivelled out of range of the furnace vessel and then, after charging of the furnace is completed, is again brought back to its initial position and lowered onto the furnace vessel.
2. Smelting. The hot and dust-laden waste gases are exhausted by direct exhaustion out of the furnace vessel via a fourth lid opening.
3. Pouring. The furnace is successively tilted until it has been completely emptied.
4. Swivelling the lid. By means of a lid raising and swivelling means, i.e., the so-called superstructure, the furnace lid is first raised vertically upwards from the furnace vessel and is then swivelled horizontally to the side.
In the direct exhaust systems on arc furnaces known at the present time the exhaust nozzle is attached to the superstructure. The lower end of the nozzle is situated above the lid opening at a distance somewhat greater than that through which the lid is raised. The free space between furnace lid and exhaust nozzle is closed by means of a cylindrical connection piece, the so-called collar, into the upper part of which the bottom end of the exhaust nozzle protrudes in a telescopic fashion and the bottom end of the collar is supported on the furnace lid above the lid opening. The collar consists of heat resistant steel sheet and its weight is negligible. Since the lower part of the collar is exposed to high thermal stress, it is normally water cooled in order to avoid oxidation and distortion. This, however, requires an additional cooling circuit with monitoring and control arrangements. When the lid is lifted the collar is either lifted by means of an additional lifting arrangement or it is lifted together with the furnace lid, since it rests on it in a freely movable fashion.
The exhaust nozzle, and thus also the collar, are arranged vertically with respect to the curved surface of the lid and normally form an included angle of 18.degree. to 20.degree. with the lid axis. If there is no additional lifting arrangement provided then, when the lid is lifted, the direction of lift of the lid and the direction of shift of the collar differ by the amount of this angle and lateral forces arise which are transmitted to the lid arch.
The surface of contact of the lid and the collar can be maintained relatively gas-tight, but this is no longer the case, for design reasons, where the upper part of the collar overlaps with the lower part of the nozzle. As a result there is uncontrolled gas escape at the transition from collar to nozzle.
The above explanations make it clear that, with the presently known direct exhaust systems on arc furnaces, the collar necessitates additional arrangements for lifting the furnace lid and also detracts from the efficiency of the flue gas exhaustion.